JP2019078550A - Crack detection method - Google Patents

Abstract

To provide a technique for an inspector to accurately evaluate a shape and a length of a crack.SOLUTION: The crack detection method detects a crack CLV generated on a surface SFC of a structure from an infrared image obtained under the irradiation of the structure STR with infrared IDW. The crack detection method includes installing an infrared camera 100 to receive infrared RFW reflected by the surface of the structure, imaging the surface using an infrared camera to obtain the infrared image, and determining whether there is a crack or not based on the intensity change of the infrared ray appearing in the infrared image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for detecting a crack generated in a structure.

  Thermoelastic effects may be used to detect whether a crack has occurred in a structure (see Patent Documents 1 to 3). The detection techniques of these documents make it possible to detect specific temperature changes at both ends of the crack using an infrared camera.

JP, 2006-98283, A Unexamined-Japanese-Patent No. 2007-163390 JP 2008-8705 A

  According to the above-described detection technique, the positions of both ends of the crack at which the thermoelastic effect is prominent are detected from the infrared image obtained from the infrared camera. That is, the two hot spots appearing in the temperature distribution in the infrared image represent the locations of the ends of the crack. The inspector can estimate that the crack is along a straight line connecting the two hot spots.

  However, the cracks do not necessarily extend linearly along the two hot spots. For example, the crack may be developing with bending between two hot spots or may be developing along a zig-zag path. In this case, the crack length will be longer than the examiner's estimate.

  Multiple cracks may be present in the infrared image. In this case, more than two hot spots appear in the infrared image. If more than two hot spots appear in the infrared image, the inspector can not determine which two of these hot spots should be associated to locate the crack.

  An object of the present invention is to provide a technique that enables an inspector to accurately evaluate the shape, length and position of a crack.

  The crack detection method according to one aspect of the present invention is used to detect a crack formed on the surface of a structure from an infrared image. In the crack detection method, an infrared camera is installed so as to receive infrared light emitted from an infrared light source artificially disposed to irradiate the structure with infrared light and reflected by the surface of the structure. The step of imaging the surface using the infrared camera to obtain the infrared image, and the crack detection method determine the presence or absence of the crack based on a change in intensity of the infrared light appearing in the infrared image. And

  According to the above configuration, the infrared camera is installed to receive the infrared light emitted from the infrared source artificially disposed to irradiate the structure with infrared light and reflected by the surface of the structure Thus, the infrared image can represent the distribution of the intensity of the infrared radiation reflected by the surface of the structure. The infrared light reflected at the cracked site and reaching the infrared camera is likely to be reflected at the non-cracked site and less than the infrared light reaching the infrared camera. Thus, the cracks will appear clearly in the infrared image representing the surface of the structure imaged by an infrared camera positioned to receive the infrared radiation reflected by the surface of the structure. In addition, cracks created on the surface of the structure may cause differences in the optical properties for infrared reflection between the two surface areas separated by the cracks. For example, if there is a difference in the slope of the two surface areas due to the occurrence of a crack, there may be a difference in the intensity of infrared light reflected from these surface areas and received by the infrared camera. In this case, a crack can appear in the infrared image as the boundary of two different surface areas in infrared intensity. An inspector can observe the infrared image to accurately grasp the shape and position of the crack generated on the surface of the structure. Since the shape of the crack clearly appears in the infrared image, the inspector can also accurately measure the length of the crack from the infrared image.

  With regard to the above configuration, the step of determining the presence or absence of the crack may include evaluating a linear portion in which the strength change appears as the crack.

  The cracks appear as linear changes in the surface shape of the structure. Therefore, the crack appears as a linear portion in the infrared image in which the intensity change of the infrared light occurs. Therefore, the crack can be evaluated as a linear site in which an infrared intensity change appears in the infrared image.

  With regard to the above configuration, the step of determining the presence or absence of the crack compares the designed surface shape of the structure with the linear portion, and the linear portion does not match the designed surface shape. Then, the method may include detecting the linear portion as the crack.

  Changes in the design surface shape of the structure also appear as changes in infrared intensity in the infrared image. If the linear portion where the infrared intensity change occurs in the infrared image does not conform to the designed surface shape of the structure, the linear portion will change the surface shape (i.e., a crack) that has subsequently occurred. It can be said that it represents. Therefore, the crack is less likely to be confused with the design surface shape change site of the structure.

  With regard to the above configuration, the crack detection method further comprises the steps of: installing the infrared source; emitting the infrared light from the infrared source to the surface of the structure to produce the reflected infrared light. May be

  According to the above configuration, since the infrared light source that emits infrared light is installed on the surface of the structure, the examiner can adjust the installation position of the infrared light source and can create appropriate imaging conditions. If an infrared source is placed near the surface of the structure, infrared light having high intensity other than that contained in sunlight will be reflected from the surface of the structure. In this case, the infrared intensity contrast tends to occur between the cracked area and the non-cracked area or between two surface areas separated by the crack, and a clear image of the crack is It becomes easy to appear in the image. If the infrared radiation reflected from the surface of the structure is too strong, the image of the crack may be blurred by the strong infrared radiation reflected around the crack. In this case, the inspector can move the infrared source away from the surface of the structure to weaken the infrared reflected around the crack. As a result, the inspector can obtain an infrared image under the reflection of infrared light of an appropriate intensity for crack evaluation.

  With regard to the above configuration, the infrared light emitted from the infrared light source to the surface of the structure may have energy that causes the surface of the structure to have a temperature increase that exceeds the temperature resolution of the infrared camera. .

  The infrared ray emitted from the infrared source is likely to hit the non-cracked area, but hard to hit the cracked area. Therefore, the temperature rise due to the infrared rays emitted from the infrared ray source is more likely to appear in the non-cracked area than the cracked area. According to the above configuration, the infrared light emitted from the infrared light source to the surface of the structure has energy that causes the surface of the structure to have a temperature increase exceeding the temperature resolution of the infrared camera, and thus the infrared light emitted from the infrared light source The difference in the temperature rise resulting from will also appear in the infrared image. Thus, the infrared image can clearly show the cracks that have occurred on the surface of the structure.

  With regard to the above configuration, the crack detection method may further include the step of applying a load to the structure to increase discontinuities generated in the surface by the cracks. The step of obtaining the infrared image may comprise imaging the surface of the structure under the load of the load.

  According to the above configuration, since the infrared image represents the surface of the structure under load, large discontinuities will appear clearly in the infrared image as cracks. Therefore, the inspector can easily grasp the crack from the infrared image.

  With regard to the above configuration, the load may be set to a value equal to or less than a rated load defined for a crane installation to be cracked as the structure.

  According to the above configuration, the load is set to a value equal to or less than the rated load set for the crane installation to be crack-tested as a structure, so the discontinuous portion where the crack is generated on the surface of the crane installation is , Under the low risk of damage to the crane equipment, get bigger.

  Regarding the above configuration, the infrared light source may be a halogen lamp.

  According to the above configuration, since the halogen lamp is used as an infrared source, the examiner can adjust the installation position of the halogen lamp and create an infrared irradiation environment suitable for obtaining an infrared image.

  The above-described technology enables an inspector to accurately evaluate the shape, position and length of a crack.

It is a conceptual diagram of the crack detection method. It is a schematic front view of a structure. It is an infrared image obtained from the crack detection method shown by FIG. It is an infrared image obtained from the crack detection method shown by FIG. It is an infrared image obtained from the crack detection method shown by FIG. It is a schematic perspective view of a crane installation.

  With regard to defect evaluation of a structure using an infrared image, it was thought that the infrared light emitted from the outside would be noise in the infrared image. However, the inventors have found that infrared radiation emitted from an infrared source artificially placed near the structure is useful for detecting cracks in the structure. The crack detection technique described below, unlike the prior art, makes it possible to detect not only the location of the ends of the crack, but also the shape of the crack. Since the shape of the crack appears clearly in the infrared image, the inspector can also measure the length of the crack with high accuracy using the infrared image.

  FIG. 1 is a conceptual view of a crack detection method. A crack detection method is described with reference to FIG.

  The solid arrows in FIG. 1 mean infrared rays (hereinafter referred to as incident wave IDW) incident on the structure STR from an infrared source artificially disposed near the structure. The dashed-dotted arrows in FIG. 1 mean infrared rays reflected by the structure STR (hereinafter referred to as a reflected wave RFW). Thicknesses of solid lines and dashed lines representing infrared rays conceptually indicate the intensity of infrared rays.

  FIG. 1 shows an infrared camera 100. The infrared camera 100 is installed to receive the reflected wave RFW. The infrared camera 100 images the surface SFC of the structure STR under irradiation of infrared light and produces an infrared image representing the surface SFC of the structure STR.

  FIG. 1 shows a crack CLV that has occurred on the surface SFC of the structure STR. A portion of the incident wave IDW is incident on the crack CLV. Since the portion where the crack CLV is not generated is flat, most of the incident wave IDW incident on the portion where the crack CLV is not generated can be incident on the infrared camera 100 as a reflected wave RFW. On the other hand, incident wave IDW which entered into crack CLV is reflected in various directions according to the complicated shape of crack surface CVS which forms the depth of crack CLV. Therefore, the ratio of the incident wave IDW incident on the crack CLV to the reflected wave RFW incident on the infrared camera 100 is that the incident wave IDW incident on the portion where the crack CLV is not incident is the reflected wave RFW incident on the infrared camera 100 It becomes smaller than the rate of becoming. For example, a portion of the incident wave IDW incident on the crack CLV repeats reflection and attenuates in the crack CLV. Therefore, while the infrared image of the position corresponding to the crack CLV is formed by the weak reflected wave RFW, the infrared image of the position corresponding to the portion where the crack CLV is not generated is formed by the strong reflected wave RFW Become. The contrast of the reflected wave RFW between the site where the crack CLV occurs and the site where the crack CLV does not occur will appear in the infrared image as a crack image representing the crack CLV.

  FIG. 2 is a schematic front view of the structure STR. The intensity distribution of infrared light around the crack CLV will be described with reference to FIGS. 1 and 2.

  FIG. 2 shows the three areas A, B, C around the crack CLV in circles drawn by dotted lines. Region A is a portion where the crack CLV is not generated. The region B is a portion where the crack CLV is generated. Region C is set at the end of the crack CLV (outside the crack CLV).

  The infrared rays emitted from the region A can be considered as the sum of the component of the reflected wave RFW described above and the infrared component emitted by the structure STR itself. Although the infrared rays emitted from the region B can be considered as the sum of the component of the reflected wave RFW and the infrared component emitted from the structure STR itself as in the region A, as described with reference to FIG. The component of the wave RFW is weaker than the component of the reflected wave RFW in the region A. Therefore, a contrast of infrared intensity is generated between the regions A and B. As mentioned above, the infrared intensity contrast appears as a crack image in the infrared image.

  The infrared radiation emitted from the region C is considered as the sum of the component of the reflected wave RFW, the infrared radiation component emitted by the structure STR itself, and the infrared radiation component produced by the temperature rise due to the thermoelastic effect. If the structure STR is made of steel or another metal, as a result of the good heat transfer in the structure STR, the hot spots resulting from the thermoelastic effect disappear in a short time. Therefore, the infrared component generated by the temperature rise due to the thermoelastic effect may not appear in the infrared image. However, as described in connection with the regions A and B, the crack image is formed by the contrast of the infrared intensity between the regions A and B, so the shape and length of the crack are the result of the thermoelastic effect It can also be evaluated from infrared images obtained after the disappearance of the hot spots.

  The incident wave IDW described with reference to FIG. 1 may be infrared light emitted from a ceiling heated by sunlight. Alternatively, the incident wave IDW may be infrared radiation emitted from a hot material (e.g., molten material, boiler or furnace) disposed near the structure STR. Further alternatively, the incident wave IDW may be a halogen lamp or another infrared irradiation device capable of emitting infrared light. These objects illustrated as infrared sources are artificially arranged. The term "arranged artificially" means arranged through the hand of the human being, excluding the tangibles that exist without the intervention of the human hand, such as the sun itself. Intended. However, the term "arranged artificially" does not exclude natural energy-irradiated artifacts or artificially arranged objects (e.g. the ceiling mentioned above).

  The incident wave IDW incident on the region A is reflected without entering the inside of the structure STR, while part of the incident wave IDW incident on the region B may enter inside the structure STR. Therefore, the temperature rise of the surface SFC of the structure STR due to the incident wave IDW incident on the region A appears more prominently than the temperature rise of the crack CLV due to the incident wave IDW incident on the region B. If the incident wave IDW has sufficient energy to generate a temperature rise on the surface SFC of the structure STR exceeding the temperature resolution of the infrared camera 100, the difference in temperature rise rate between the regions A and B is also a crack image It will appear.

  Figures 3A-3C are infrared images obtained from the crack detection method described above. An infrared image is described with reference to FIGS. 3A to 3C.

  The surface of the structure shown in FIG. 3A is covered by a coating. As a result of the cracks occurring in the structure, the coating is raised along the cracks. As a result of the coating bulge along the crack, the infrared rays incident on the crack initiation site reflect in various directions. Therefore, the amount of infrared light reflected at the cracked site is smaller than the amount of infrared light reflected at the non-cracked site. That is, a difference in the amount of infrared light captured by the infrared camera occurs between the cracked site and the non-cracked site. The difference in the amount of infrared light captured by the infrared camera appears as a crack image representing a crack, as shown in FIG. 3A.

  For the infrared image shown in FIG. 3B, there is a step between the area above the crack and the area below the crack. Infrared rays radiated from the outside are less likely to be incident on discontinuous sites where cracks have occurred, such as steps. In addition, the infrared radiation propagating from the cracked discontinuity to the infrared camera tends to be less than the infrared radiation propagating from the non-cracked region to the infrared camera. The difference between the amount of incident infrared radiation and / or the amount of reflection of infrared rays between the discontinuity where the crack has occurred and the other region appears as a crack image representing a crack, as shown in FIG. 3B.

  The cracks appearing in the infrared image of FIGS. 3A and 3B are developing linearly, while the cracks in the infrared image shown in FIG. 3C are highly curved. Unlike the prior art, the crack detection method described above allows not only the location of the crack edge but also the shape of the crack to be shown in the infrared image. Therefore, the examiner can also accurately measure the length of the crack generated in the structure from the infrared image.

  The vertical band shown on the right side of the infrared image in FIG. 3C represents the surface temperature of the structure converted from the amount of infrared light captured by the infrared camera. The examiner can analyze the temperature distribution on the surface of the structure with reference to the temperature division shown in the vertical band. As a result of the occurrence of cracks, micro deformation (e.g., surface waviness) of the surface shape of the structure may occur. Since a crack makes two regions separated by a crack discontinuous, surface shape differences may also occur between these regions. When the inspector analyzes the temperature distribution of the infrared image of FIG. 3C, a difference can be found in the temperature distribution characteristics between the area above and below the crack. The inspector can also detect the occurrence of deformation of the surface shape of the structure from the difference in temperature distribution characteristics between these regions. Thus, the crack detection method described above makes it possible to give the inspector more information than in the prior art.

  As shown in FIGS. 3A to 3C, the cracks appear as a change in the intensity of infrared radiation that appears in the infrared image. Therefore, the examiner can refer to the infrared image and determine the portion where the intensity change of the infrared light appears as a crack. However, if the designed surface shape of the structure is not flat, the non-linear uneven portion of the designed surface shape may cause the intensity change of infrared light in the infrared image. Since the crack is a linear or curvilinear change of the surface of the structure, the examiner may not evaluate the non-linear strength change site in the infrared image as a crack. In addition, the examiner can compare the infrared image to the designed surface shape of the structure to determine whether the intensity change site appearing in the infrared image represents a crack. If, by design, a linear change in infrared intensity appears at a position where no shape change appears on the surface of the structure, the examiner can judge the portion where the linear change appears as a crack.

  FIG. 4 is a schematic perspective view of the crane installation CRF. The crack detection method is further described with reference to FIG.

  The crane installation CRF comprises two runway girders RWG, two crane girder CRBs, two saddles SDL and a club trolley CTR. The two runway girders RWG extend substantially parallel. The two saddles SDL are respectively mounted on the two runway girders RWG and can move along these runway girders RWG. The two crane girders CRB extend substantially perpendicularly to the runway girder RWG between the two saddles SDL. Therefore, the crane girder CRB can be moved in the extending direction of the runway girder RWG together with the saddle SDL. The Club Troli CTR is supported by two crane girder CRBs. Therefore, the club trolley CTR can move in the extending direction of the runway girder RWG together with the crane girder CRB and the saddle SDL. In addition, the club trolley CTR can also be moved along the two crane girders CRB in a direction perpendicular to the runway girder RWG extension direction.

  The above-mentioned crack detection method can be suitably used for detection of a crack generated in a runway girder RWG or a crane girder CRB. FIG. 4 shows the infrared camera 100 installed on the stage STG suspended from the club trolley CTR. The halogen lamp 200 is installed on the stage STG next to the infrared camera 100 as an infrared source for emitting infrared light. The infrared camera 100 and the halogen lamp 200 are directed to one of two runway Garda RWGs. Therefore, the infrared image obtained from the infrared camera 100 can be used to inspect a crack that has occurred on one of the two runway girders RWG. The inspector can also change the orientation of the infrared camera 100 and the halogen lamp 200, and detect a crack formed on the surface of the other runway girder RWG and the two crane girders CRB.

  If the saddle SDL is moved along the runway girder RWG, the field of view of the infrared camera 100 moves in the longitudinal direction of the runway girder RWG. During this time, the inspector can use the infrared camera 100 to continuously image the surface of the runway girder RWG in the longitudinal direction of the runway girder RWG. Therefore, the inspector can inspect the entire runway girder RWG in a short time to determine whether or not a crack has occurred in the runway girder RWG.

  The weights of the two crane girders CRB, the two saddles SDL, the club trolley CTR, the stage STG, the infrared camera 100 and the halogen lamp 200 are loads applied to the runway girder RWG. If the runway girder RWG is cracked, the load may also increase discontinuities (eg, step or crack width) caused by the crack. Thus, the discontinuities created by the crack are infrared images obtained under the loaded weight of two crane girders CRB, two saddles SDL, club trolley CTR, stage STG, infrared camera 100 and halogen lamp 200 It becomes easy to appear clearly.

  A weight may be placed on the stage STG. If the sum of the weights of the stage STG, the infrared camera 100 and the weight reaches the rated load defined for the crane installation CRF, the maximum allowable load will be applied to the runway girder RWG. As a result, the discontinuities created by the cracks may be maximized. Thus, the cracks are more likely to appear clearly in the infrared image. The load applied to the crane installation CRF for crack definition may not be the rated load. The operator may set the load applied to the crane installation CRF to a value equal to or less than the rated load, in consideration of the sharpening of the crack and the safety of the crane installation CRF.

  Conventional inspection techniques that rely on the thermoelastic effect require dynamic loading because they need to generate a singular stress field at the end of the crack. On the other hand, since the above-mentioned crack detection method uses a load in order to expand the discontinuous part generated by the crack, the load may be a static load or a dynamic load.

  The infrared camera 100 may be installed such that the field of view of the infrared camera 100 includes an area to which a large load is applied. In this case, a clear crack image tends to appear in the infrared image.

  The inspector may adjust the position of the halogen lamp 200 before the crack inspection. If the examiner refers to the infrared image obtained before the crack examination and determines that the intensity of the infrared ray is too strong, the examiner may move the halogen lamp 200 away from the runway girder RWG. If the examiner determines that the intensity of infrared light is too weak, the examiner may bring the halogen lamp 200 closer to the Runway Garda RWG. If the output of the halogen lamp 200 is adjustable, the examiner may operate the halogen lamp 200 to adjust the output of the halogen lamp 200. As a result, an appropriate infrared radiation environment is created.

  When the site likely to be cracked is known, or when the site to be examined is previously determined, the examiner may cause the infrared camera 100 to face the target site. At this time, the inspector may place the halogen lamp 200 on the stage STG so that the optical axis of the halogen lamp 200 intersects the optical axis of the infrared camera 100. Alternatively, the inspector may place the halogen lamp 200 on the stage STG such that the optical axis of the halogen lamp 200 is parallel to the optical axis of the infrared camera 100. The principle of the present embodiment is not limited to a specific relationship between the optical axis of the halogen lamp 200 and the optical axis of the infrared camera 100.

  The principles of the above-described embodiments are applicable to crack inspection of various inspection objects.

100 ···················· infrared camera 200 ···················· halogen lamp (infrared source)
CLV ···················· crack CRF ···················· crane equipment IDW ···· · · · · · · · · · · · · · Incident wave (infrared)
RFW ···················· reflected wave (infrared)
SFC ························································· Structure

Claims (8)

A crack detection method for detecting a crack generated on a surface of a structure from an infrared image, comprising:
Installing an infrared camera so as to receive infrared light emitted from an infrared source artificially arranged to irradiate the structure with infrared light and reflected by the surface of the structure;
Imaging the surface using the infrared camera to obtain the infrared image;
Determining the presence or absence of the crack based on a change in intensity of the infrared light appearing in the infrared image. The crack detection method according to claim 1, wherein the step of determining the presence or absence of the crack includes evaluating a linear portion in which the strength change appears as the crack. The step of determining the presence or absence of the crack compares the designed surface shape of the structure with the linear portion, and if the linear portion does not match the designed surface shape, the line The crack detection method according to claim 2, comprising detecting a cracked portion as the crack. Installing the infrared source;
The crack detection method according to any one of claims 1 to 3, further comprising: emitting the infrared light from the infrared light source to the surface of the structure to produce the reflected infrared light. The infrared light emitted from the infrared light source to the surface of the structure has energy that causes the surface of the structure to have a temperature increase exceeding the temperature resolution of the infrared camera. The crack detection method as described in a term. The method further comprises the step of applying a load to the structure to increase discontinuities that the crack has caused on the surface,
The crack detection method according to any one of claims 1 to 5, wherein the step of obtaining the infrared image includes imaging the surface of the structure under a load of the load. The crack detection method according to claim 6, wherein the load is set to a value equal to or less than a rated load defined for a crane installation to be crack-tested as the structure. The crack detection method according to any one of claims 1 to 7, wherein the infrared light source is a halogen lamp.

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